Segregated phase comparison relaying systems of the type illustrated herein are described and claimed in U.S. Pat. No. 3,893,008, dated July 1, 1975. No direct transfer-trip function is shown or described in said patent although this function has been provided in other relaying systems.
In accordance with this invention, the signal which would normally be used to determine the current flow condition at the two ends of the protected network section of a three-phase power transmission network are altered to provide a combination of signals which would normally never occur at all or never occur for the predetermined time intervals necessary to time out the direct transfer-trip timer.